U.S. patent number 5,672,546 [Application Number 08/566,624] was granted by the patent office on 1997-09-30 for semiconductor interconnect method and structure for high temperature applications.
This patent grant is currently assigned to General Electric Company. Invention is credited to Robert John Wojnarowski.
United States Patent |
5,672,546 |
Wojnarowski |
September 30, 1997 |
Semiconductor interconnect method and structure for high
temperature applications
Abstract
A method for interconnecting at least one semiconductor chip (14
or 36) having chip pads (16 or 38) includes applying a removable
polymer layer (22 or 44) over the chip; forming vias (26 or 50) in
the polymer layer aligned with predetermined chip pads; depositing
a pattern of electrical conductors (28 or 52) over the polymer
layer and into the vias; and removing the polymer layer. Prior to
applying the polymer layer, the chip can be attached to a substrate
by attaching a backside of the chip in a substrate chip well using
a high temperature chip attach material (12) or by inserting the
chip in a through hole of the substrate and applying a
metallization plane (54) supporting the backside of the chip and at
least a portion of the substrate. The substrate can have substrate
metallization (18 or 42) substantially planar to the chip pads with
the step of applying the polymer layer over the at least one
semiconductor chip including applying the removable polymer layer
over the substrate, and the step of forming vias in the polymer
layer including forming vias aligned with predetermined portions of
the substrate metallization.
Inventors: |
Wojnarowski; Robert John
(Ballston Lake, NY) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
24263681 |
Appl.
No.: |
08/566,624 |
Filed: |
December 4, 1995 |
Current U.S.
Class: |
438/107;
257/E21.705; 257/E23.17; 257/E23.178; 438/125; 438/126 |
Current CPC
Class: |
H01L
23/5381 (20130101); H01L 23/5389 (20130101); H01L
24/24 (20130101); H01L 24/82 (20130101); H01L
25/50 (20130101); H01L 23/5385 (20130101); H01L
2224/24225 (20130101); H01L 2224/24227 (20130101); H01L
2224/73267 (20130101); H01L 2224/92244 (20130101); H01L
2924/01013 (20130101); H01L 2924/01042 (20130101); H01L
2924/01074 (20130101); H01L 2924/12044 (20130101); H01L
2924/14 (20130101); H01L 2924/15153 (20130101); H01L
2924/15165 (20130101); H01L 2924/15165 (20130101); H01L
2924/15153 (20130101); H01L 2224/24227 (20130101); H01L
2924/15165 (20130101); H01L 2924/01005 (20130101); H01L
2924/01006 (20130101); H01L 2924/01033 (20130101); H01L
2924/014 (20130101); H01L 2224/48472 (20130101); H01L
2224/24137 (20130101); H01L 2224/32225 (20130101); H01L
2224/32245 (20130101); H01L 2924/12042 (20130101); H01L
2924/12042 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
H01L
21/70 (20060101); H01L 21/98 (20060101); H01L
23/52 (20060101); H01L 23/538 (20060101); H01L
021/60 () |
Field of
Search: |
;437/51,182,205,209 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4289846 |
September 1981 |
Parks et al. |
4418470 |
December 1983 |
Naster et al. |
4722914 |
February 1988 |
Drye et al. |
4783695 |
November 1988 |
Eichelberger et al. |
4835704 |
May 1989 |
Eichelberger et al. |
4894115 |
January 1990 |
Eichelberger et al. |
4933042 |
June 1990 |
Eichelberger et al. |
5102829 |
April 1992 |
Cohn |
5149662 |
September 1992 |
Eichelberger |
5188984 |
February 1993 |
Nishiguchi |
5198385 |
March 1993 |
Devitt et al. |
5306670 |
April 1994 |
Mowatt et al. |
5348607 |
September 1994 |
Wojnarowski et al. |
5353498 |
October 1994 |
Fillion et al. |
5524339 |
June 1996 |
Gorowitz et al. |
5548099 |
August 1996 |
Cole, Jr. et al. |
|
Primary Examiner: Picardat; Kevin
Attorney, Agent or Firm: Agosti; Ann M. Snyder; Marvin
Claims
What is claimed is:
1. A method for interconnecting at least one high temperature
semiconductor chip having chip pads, the method comprising:
applying a removable polymer layer over the at least one
semiconductor chip;
forming vias in the removable polymer layer aligned with the chip
pads;
depositing a flexible pattern of electrical conductors capable of
withstanding high temperatures over the removable polymer layer and
into the vias; and
removing the removable polymer layer.
2. The method of claim 1, wherein the pattern of electrical
conductors is a titanium/tungsten alloy or a composite of titanium
and molybdenum layers.
3. The method of claim 1, wherein the pattern of electrical
conductors includes S-shaped conductor line patterns.
4. The method of claim 1, further including the step of, prior to
applying the removable polymer layer, attaching a backside of the
at least one semiconductor chip in a chip well of a substrate using
a high temperature chip attach material.
5. The method of claim 4, wherein
the substrate has substrate metallization, the chip pads and the
substrate metallization being substantially planar,
the step of applying the removable polymer layer over the at least
one semiconductor chip includes applying the removable polymer
layer over the substrate, and
the step of forming vias in the removable polymer layer includes
forming vias aligned with portions of the substrate
metallization.
6. The method of claim 1, further including the step of, prior to
applying the removable polymer layer, inserting the at least one
semiconductor chip in a through hole of a substrate.
7. The method of claim 6, wherein
the substrate has substrate metallization, the chip pads and the
substrate metallization being substantially planar,
the step of applying the removable polymer layer over the at least
one semiconductor chip includes applying the removable polymer
layer over the substrate, and
the step of forming vias in the removable polymer layer includes
forming vias aligned with portions of the substrate
metallization.
8. The method of claim 7, wherein the pattern of electrical
conductors includes dips in conductor line patterns.
9. The method of claim 6, wherein the steps of applying the
removable polymer layer and inserting the at least one
semiconductor chip include:
holding the removable polymer layer substantially planar;
positioning the substrate on the removable polymer layer; and
positioning the at least one semiconductor chip in the through hole
with chip pads facing the removable polymer layer.
10. The method of claim 6, further including:
positioning buffer material in the through hole between the at
least one semiconductor chip and the substrate;
applying a metallization plane over a backside of the at least one
semiconductor chip and at least a portion of the substrate; and
removing the buffer material.
11. The method of claim 10, wherein the steps of removing the
removable polymer layer and removing the buffer material occur
simultaneously.
Description
BACKGROUND OF THE INVENTION
Wire bonding techniques for interconnecting high temperature die
materials such as silicon carbide can be unreliable because the
mechanical joints of wire bonds are not designed for use in
temperatures exceeding about 150.degree. C. and tend to degrade at
temperatures above 200.degree. C.
Another limitation of wire bonding is the fact that high
temperature metals such as molybdenum are not compatible with
conventional wire bonding. Aluminum has been added to the
molybdenum in an attempt to create a wire bondable region, but the
bonds remain unreliable at high temperatures.
In one form of high density interconnect (HDI) circuit module, an
adhesive-coated polymer film overlay having via openings covers a
substrate which can support integrated circuit chips in chip wells.
The polymer film provides an insulated layer upon which is
deposited a metallization pattern for interconnection of substrate
metallization and/or individual circuit chips through the vias.
Methods for performing an HDI process using overlays are further
described in Eichelberger et al., U.S. Pat. No. 4,783,695, issued
Nov. 8, 1988, and in Eichelberger et al., U.S. Pat. No. 4,933,042,
issued Jun. 12, 1990. Generally a plurality of polymer film
overlays and metallization patterns are used.
This type of HDI circuit module provides efficient use of space and
flexibility of interconnection patterns. However, most polymers are
not capable of withstanding sustained high temperatures such as
300.degree. C. and above without severe degradation.
SUMMARY OF THE INVENTION
It would be advantageous to have a fabrication process that both
interconnects semiconductor die efficiently and is capable of
withstanding continuous high temperature environments. In the
present invention, a temporary laminate structure with a removable
polymer layer is used to facilitate deposition of metallization
patterns, and the polymer layer is later removed (dissolved or
otherwise etched away). The present invention is especially useful
with semiconductor die comprising materials such as silicon
carbide, for example, which are able to withstand high
temperatures.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the invention believed to be novel are set forth
with particularity in the appended claims. The invention itself,
however, both as to organization and method of operation, together
with further objects and advantages thereof, may best be understood
by reference to the following description taken in conjunction with
the accompanying drawings, where like numerals represent like
components, in which:
FIG. 1 is a sectional side view of a polymer layer overlying a
substrate supporting a chip in a chip well.
FIG. 2 is view similar to that of FIG. 1 further showing vias in
the polymer layer and a pattern of electrical conductors extending
through the vias.
FIGS. 3 and 3a enlarged partial views of the polymer layer and
pattern of electrical conductors shown in FIG. 2.
FIG. 4 is a view similar to that of FIG. 2 showing the substrate,
chip and pattern of electrical conductors after the polymer layer
has been removed.
FIG. 5 is a top view of several chips interconnected using the
approach shown in FIGS. 1-4.
FIG. 6 is a sectional side view of a chip within a substrate
through hole with buffer material disposed between the chip and
substrate and a deposited metallization plane on the backside of
the chip.
FIG. 7 is a view similar to that of FIG. 6 after the chip and
substrate have been turned over and a pattern of electrical
conductors has been applied.
FIG. 8 is a view similar to that of FIG. 7 after the removal of the
buffer material.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
FIG. 1 is a sectional side view of a removable polymer layer 22
overlying a substrate 10 supporting a semiconductor chip 14 in a
chip well 24. The substrate comprises a suitable structural
material which can withstand a high temperature environment.
Preferably the substrate comprises a ceramic material such as
alumina, for example. The substrate can optionally include
substrate metallization 18 and 20 thereon to facilitate further
interconnections. The substrate can further include, if desired,
multiple layers of ceramic having metallization patterns
therebetween (not shown).
Chip 14 preferably comprises a semiconductor die or device capable
of operation in a high temperature environment, and in one
embodiment the chip comprises silicon carbide. The substrate
metallization 18 and chip pads 16 are substantially planar to
reduce potential stresses on the later applied pattern of
electrical conductors and both may comprise metals capable of
withstanding high temperatures. Appropriate metals include alloys
such as titanium/tungsten and composite layers such as titanium
coated with molybdenum, for example. The chip can be attached to
the substrate using a high temperature chip attach material 12
which may comprise a solder-braze reflow material, for example.
Polymer layer 22 comprises a dissolvable material such as a
polyester, a solder resist, or ULTEM.TM. polyetherimide resin
(ULTEM is a trademark of General Electric Company), for example. If
polymer layer 22 comprises a polyetherimide resin, preferably a
layer having a thickness ranging from 0.3 mils to 5 mils is
laminated in a vacuum chamber.
FIG. 2 is view similar to that of FIG. 1 further showing vias 26
formed in the polymer layer and a pattern of electrical conductors
28 extending through the vias. The vias can be formed by any
appropriate method and in one embodiment are laser ablated by a
technique such as described in Eichelberger et al., U.S. Pat. No.
4,894,115, issued Jan. 16, 1990.
The via holes can then be plasma ashed (or reactive ion etched)
with a 20% CF.sub.4 and 80% O2 solution to remove any carbonized
polymer debris and to clean the surfaces of the exposed chip pads
and substrate metallization. The exposed chip pads and substrate
metallization can be back sputtered for further cleaning.
Preferably the surface area of each bottom of a via hole will be as
large as possible so as to aid in establishing a strong mechanical
and electrical contact. In one embodiment wherein the chip pads
have sides ranging from two to five mils, the via holes have square
bottoms with sides ranging from one to four mils.
Pattern of electrical conductors 28 can be applied, for example, by
sputter depositing high temperature metals under vacuum conditions.
Metals which can adhere well to underlying chip pads and substrate
metallization and can withstand high temperatures include alloys
such as titanium/tungsten and composite layers such as titanium
coated with molybdenum, for example.
Typically the total thickness of the metallization ranges from two
to twenty micrometers, with an underlying seed layer portion having
a thickness of about 1000 .ANG.. The minimum required thickness of
the metallization depends on the amount of current expected, as
well as the width of metallization runs in the pattern of
electrical conductors.
Depending on the thickness of the pattern of electrical conductors
and the properties of polymer layer 22, it may be preferable to
sputter the metallization in several stages with cooling periods in
between to avoid melting or distorting the polymer layer.
Patterning of the applied metallization can be accomplished using
conventional photoresist and etching techniques. Mask patterning
can be used for batch manufacturing. Metallization patterning can
be controlled precisely using a technique such as the adaptive
lithography described in Eichelberger et al., U.S. Pat. No.
4,835,704, issued May 30, 1989.
FIG. 3 is an enlarged partial view of polymer layer 22 and pattern
of electrical conductors 28 shown in FIG. 2. Although FIGS. 1-2, 4,
and 6-8 show the polymer layer and pattern of electrical conductors
as being flat, in practice, a slight dip 22a will typically be
present in the area between chip 14 and substrate 10 after the
attachment of the polymer layer. This will create a corresponding
dip 28a in the pattern of electrical conductors. This dip is useful
because it provides a stress relieving structure which has
increased length and flexibility to accommodate differences which
may exist in the coefficients of thermal expansion of the chip and
substrate. As shown in FIG. 3a another method for increasing
flexibility is to use longer line patterns, such as S-shaped lines
328, instead of straight lines.
FIG. 4 is a view similar to that of FIG. 2 showing the substrate
10, chip 14, and pattern of electrical conductors 28 after the
polymer layer has been removed. The polymer layer can be removed by
any appropriate process, and in one embodiment is removed by
dissolution in a solvent. When the polymer layer comprises a
polyetherimide resin, for example, the polymer layer can be
dissolved using methylene chloride, anisole, n-methyl-pyrrolidone,
acetophenone, ortho dichloro benzene, cresol, cresylic acid, and
concentrated sulfuric acid. The reactivity of the polymer layer in
a solvent is typically increased by heating, so it is useful to
apply the solvent using a hot spray technique, for example. Polymer
removal approaches which do not require solvents include plasma
etching and RIE (reactive ion etching), for example.
After the polymer layer has been removed, the pattern of electrical
conductors becomes a plurality of integral interconnect segments
each having a shelf portion 29 spaced apart from the chip and
substrate and coupled to the chip and/or substrate metallization by
leg portions 31 which remain in the prior locations of vias which
had been formed in the polymer layer.
Although the description of FIGS. 1-4 has been in terms of a single
polymer layer and pattern of electrical conductors, a structure
having multiple layers of electrical conductor patterns can easily
be fabricated by these same techniques so that one or more
additional patterns of electrical conductors are coupled to the
first pattern. An additional polymer layer (not shown) overlying
the first polymer layer and pattern of electrical conductors would
need to have a thickness sufficient to prevent any shorting between
by the additional pattern of electrical conductors after the
polymer layers are removed.
FIG. 5 is a top view of several chips 14 interconnected using the
approach shown in FIGS. 1-4. Each chip can be coupled to substrate
metallization 18 and 20 which in turn can be coupled to another
chip or through a seal ring 32 to other metallization runs 34, for
example. Alternatively, the chips can be coupled directly together
through a portion 28a of the pattern of electrical conductors
28.
FIG. 6 is a sectional side view of a high temperature semiconductor
chip 36 within a substrate 40 through hole 41 with buffer material
46 between the chip and substrate and a deposited metallization
plane 54 on the backside of the chip.
In one embodiment, a removable polymer layer 44 is kept
substantially planar by a frame 43. Polymer layer 44 may comprise
materials such as those described with respect to polymer layer 22
of FIG. 1. The substrate is then positioned on the removable
polymer layer, and the semiconductor chip is inserted in the
through hole with chip pads 38 facing the removable polymer layer.
The polymer layer can be heated for softening (if needed) to
provide adhesion of the polymer layer to the semiconductor chip and
the substrate, and the polymer layer can later be solidified. As
described by Wojnarowski et al., U.S. Pat. No. 5,348,607, issued
Sep. 20, 1994, for example, in one method in which heating is not
required, chips are attached to a surface with glue and the surface
is then coated with a solvented thermoplastic polymer solution and
dried.
Buffer material 46 is inserted between the chip and the substrate
to prevent metallization plane 54 from extending too deep in the
through hole between the chip and the substrate. The buffer
material need not extend through the entire space between the chip
and substrate. In fact, it is useful to not fill the through hole
completely with buffer material so that dips such as those
discussed with respect to FIG. 3 can be formed to increase the
flexibility of the pattern of electrical conductors.
In one embodiment, the buffer material is injected after the chip
and substrate are positioned on polymer layer 44. The buffer
material comprises a removable material, preferably in a form
capable of being poured. If the buffer material is poured as a
liquid, it can then be solidified. For ease of later removal, it is
convenient if the buffer material comprises material the same as
the polymer layer or is otherwise capable of simultaneous removal.
In one embodiment, the buffer material comprises a polyetherimide
resin.
The substrate/buffer material/chip surface can be cleaned and or
planarized by a process such as grinding or plasma etching which
preferably occurs at a point in time when the buffer material is
solid. These processes are useful in the event that buffer material
has spilled on the substrate or chip, or in the event that the
surfaces are nonplanar.
Metallization plane 54 can be applied as discussed with respect to
pattern of electrical conductors 28 of FIG. 2 in a similar manner
with high temperature metals having low coefficients of thermal
expansion such as titanium/tungsten and titanium coated with
molybdenum. Because the metallization plane is adjacent the chip
and substrate it need not be as thick as the pattern of electrical
conductors, and in one embodiment the thickness is about 10
micrometers. The metallization plane can be applied by techniques
such as sputtering, plasma spraying, and/or electroplating. The
metallization plane may be left as a blanket coating on the
substrate and chip, or, if desired, the metallization plane can be
patterned in area around the chip, as shown in FIGS. 7 and 8.
The buffer material and metallization plane need not be applied in
the specific sequence described above. For example, the buffer
material and metallization may be added after applying pattern of
electrical conductors 52 or, alternatively, before applying polymer
layer 44, if desired.
FIG. 7 is a view similar to that of FIG. 6 after the chip and
substrate have been turned over and pattern of electrical
conductors 52 has been applied. Vias 50 and pattern of electrical
conductors 52 can be formed in the manner discussed with respect to
vias 26 and pattern of electrical conductors 28 of FIG. 2. FIG. 7
further illustrates the use of an additional via 50a for structural
support purposes (instead of for interconnection to a chip pad or
substrate metallization). Such additional via is especially useful
for any long portions of the pattern of electrical conductors.
FIG. 8 is a view similar to that of FIG. 7 after the removal of
polymer layer 44 and buffer material 46. The polymer layer can be
removed by processes such as those discussed with respect to FIG.
4. If the buffer material is the same as or compatible with the
polymer layer, the buffer material can be removed simultaneously by
a single solvent. To aid in removal of the buffer material,
techniques such as solvent warmed plasma etching and high heat
firing can be used.
Metallization plane 54 provides a useful bond for attaching the
chip and substrate which can be more reliable than the high
temperature chip attach material 12 of FIG. 2 and does not require
brazing, solder flux, or any other high temperature technique for
chip attach. Furthermore, the metallization plane, especially if
patterned as shown in FIGS. 7 and 8, offers increased flexibility
for varying coefficients of thermal expansion between the chip and
substrate.
While only certain preferred features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *